The invention relates generally to an apparatus for coating glass and, in particular, to a temperature controlled distributor beam for chemical vapor deposition on glass.
One method of coating flat glass is by contacting the glass with a gaseous coating material at substantially atmospheric pressure. However, it has been difficult to achieve uniform coatings on a moving glass ribbon by known techniques. In U.S. Pat. No. 3,850,679, it is proposed to enhance the uniformity of films produced by chemical vapor deposition by directing coating gas onto the glass surface through a nozzle at a Reynolds number of at least 2,500. For speed coating a continuous ribbon or sheet of glass, a Reynolds number of at least 5,000 for the flowing gas is recommended. The use of a Reynolds number above 2,500 means that the gas flow is turbulent.
A more satisfactory method of obtaining a uniform coating is to cause the coating gas to flow substantially parallel to the surface of a moving ribbon of glass to be coated under laminar flow conditions as opposed to turbulent flow conditions. A method and apparatus for achieving laminar flow conditions is disclosed in U.S. Pat. No. 4,469,045. The coating gas is directed onto a surface to be coated by a distributor extending across the upper surface of a moving ribbon of glass and across the direction of movement of the ribbon. This device is especially useful for applying a coating from a gas which reacts on contacting the hot glass surface to deposit a coating material on the glass, such as a metal vapor. The temperature of the gas supply and the distributor is preferably kept sufficiently high to prevent condensation of the coating gas, but sufficiently low to prevent any substantial decomposition or other deleterious reactions of the coating gas before the coating gas reaches the glass surface.
The precise temperature control required for proper coating is difficult to obtain. Current systems attempt to maintain the optimum temperature by cooling the distributor with high pressure steam, water, oil, or gas. Such systems are complicated, expensive and often dangerous to operate.